1. Field of the Invention
The present invention relates to a medicinal tablet forming machine and method for using the machine. More particularly, the present invention relates to a machine for forming a two-layer, generally cylindrical, vertically-compressed and vertically-aligned bandless tablet.
2. Description of the Prior Art
It is well known in the art that a tablet can be formed by compressing powder in a vertical press. It is also known that by application of appropriate metering mechanisms, a tablet composed of layers of at least two different materials can be formed in a vertical press. Such multi-component tablets formed in accordance with the prior art are frequently characterized by an intermixing of the components at the interface of the layers. Depending upon the components of the medicinal tablet, the intermixing of the components at tile interface of the layers may produce adverse results caused by long term incompatibility of the components in one another.
In the prior art, the manufacture of generally cylindrical multi-component tablets is accomplished in a vertical press with the longitudinal axis of the formed tablet being shorter than the diameter of the tablet. A vertically disposed generally cylindrical tablet having a longitudinal axis greater than the diameter suffers from the problem of incomplete hardening of the tablet during pressing. Surface tension which develops between the powder and the die cavity wall frequently prevents the complete compaction of the powder. The resulting tablet lacks sufficient strength in its midsection to withstand normal stresses, thereby causing the tablet to crack or break.
Because prior art cylindrical tablets require large diameters relative to the tablet volume, space is sacrificed on the die station. As a result, fewer tablets can be formed for a given die station size as the diameter of a tablet is increased relative to the longitudinal axis of the tablet.
A further problem associated with the prior art manufacture of multicomponent tablets concerns the transverse compression of the tablet. Such compression produces a band which runs along the surface of the tablet at the interface of the different components. In order to camouflage this band, cylindrical tablets are generally provided with unique geometries which incorporate the band in the design. A typical example of a prior art multiple component cylindrical tablet is shown in FIGS. 1a, 1b and 1c.
Because of the shape of the tablets shown in FIGS. 1a, 1b and 1c the layers of powders are disposed along the longitudinal axis of the tablet. This results in a tablet having a large surface area interface between the different components, affording a great opportunity for intermixing of the two layers.
It is an object of this invention to provide a generally cylindrical two-layer tablet in which the longitudinal axis of the tablet is greater than the tablet diameter.
It is a further object of this invention to provide an apparatus for forming a two-layer cylindrical tablet in which the longitudinal axis of the tablet is greater than the tablet diameter.
It is a still further object of this invention to provide a method for forming a two-layer cylindrical tablet in which the longitudinal axis of the tablet is greater than the tablet diameter.